Like an airplane that doesn't register on radar, "stealth students" slip in and out of classrooms every day, contributing little, if anything: They're the ones who don't respond when an instructor asks questions or don't ask questions themselves when they need clarification. To the instructor, it's like posing a question to an empty room, which is philosophically interesting but doesn't really help the learning process. Some stealth students are quiet by nature; others are afraid to make a mistake in front of the class; and still others just seem to freeze like a deer in headlights. Unfortunately, stealth students hurt both themselves and the class when they don't participate.
As I lecture, I spend a great deal of time analyzing facial expressions to see whether my students are understanding what I'm teaching. People usually have some sort of body language that tells me when they're confused, puzzled, or lost. If I notice a change in Joe's facial expression, for example, I take a moment to ask him a question to gauge what's going on in his mind. Quite often, when Joe vocalizes his thoughts, it helps everyone in the class because other students have similar thoughts.
When a student doesn't give any nonverbal cues about how the lecture is progressing, I fall back on questions that relate to what I'm teaching. If I have Jane summarize in her own words what I just taught, I can gauge whether my presentation is making sense. Once again, I know from experience that if one person doesn't understand something, others probably don't either. Along the same lines, questions that a student volunteers typically are on others' minds as well; therefore, students who ask questions (that are on topic) help the entire class make sense of what I'm covering.
Stealth students hurt the class in three ways: they don't give nonverbal cues, don't respond when asked a question, and don't volunteer any questions. Personally, I find stealth students the most frustrating because I use all the feedback I get to tailor how and what I teach. The single greatest benefit of instructor-led training is the interaction with the instructor and other students, and stealth students undermine that benefit by discouraging a dialog.
How can you avoid being a stealth student? You can, quite simply, ask questions. All teachers like questions from students because questions show that the students are listening and attempting to process what the instructor is teaching. If it isn't in your nature to speak out in public, approach the instructor during a break or after class. I've even considered making instant messaging (IM) available in class for those students who would rather type a question than ask it in front of the whole class. Well-considered questions can help direct the flow of class as well as affect how the instructor presents the material. Just remember that if you don't show up on your instructors' radar screens, you can't blame them if they ignore you.